The use of satellite-based and aerial-based imagery of the Earth is popular among government and commercial entities. One of the many applications of such imagery is for shallow water bathymetry. Bathymetry is the study of the underwater depth of bodies of water, such as oceans, seas, or lakes. Bathymetric information can be used to make bathymetric charts or maps for navigation purposes, as well as for many other uses.
While other methods are possible, there are three primary means for determining the depth at various points in a body of water. The first is beam sounding (also known as echosounding or SONAR), typically performed from a boat. This method is highly accurate but is the most expensive, costing in the range of $5,000 per square kilometer of area for which the depth is determined. The second method involves laser ranging (LIDAR), typically performed from an aircraft. This method is less accurate than, but also less expensive than, beam sounding, costing in the range of $2,000 per square kilometer of area for which the depth is determined. The third method involves analyzing overhead or satellite imagery to determine depth. This method has been the least accurate of the three methods and it is only effective for relatively shallow depths (e.g., down to 30 meters), and only for water clarity between clear and relatively turbid, but it is the least expensive of the three methods, costing in the range of $150 per square kilometer of area for which the depth is determined.
Typically, bathymetry from satellite imagery is performed by comparing the relative absorption of light in different color bands (e.g., green, blue, and coastal blue (e.g., bands in the range of 400-500 nanometers and thereabouts). The absorption of light by water causes the shallow water depth limitation for satellite imagery techniques. Furthermore, imaging is typically only performed in daylight. Also, satellite imagery is limited to conditions where the water is relatively clear, as the image sensors to a large extent see much like humans do. It would be desirable to increase the accuracy of bathymetry from overhead imagery.
It is against this background that the improvements disclosed herein have been developed.